1. Field of the Invention
The present invention relates to a cable modem, and more particularly to a cable modem that can prevent a modem signal from transferring to an HFC (Hybrid Fiber Coaxial Network) when an internal circuit of the cable modem operates abnormally.
2. Description of the Related Art
An HFC network using a cable modem is a shared media network, meaning that if an unwanted signal comes from a cable modem connected to a network, or if the cable modem operates abnormally and thus, generates a signal with a particular frequency, the entire system is fatally influenced and in the worst case, the network is likely to be shut down. A related art cable modem controls the transferring of a burst signal to the HFC network, by using an enable signal of a PGC (Programmable Gain Controller) that adjusts or controls signal intensity of the cable modem.
A burst signal is used for an up-stream signal of the cable modem to reduce the influence of an unwanted signal on the HFC network using the shared media. The enable signal of the PGC is used to turn on and turn off the burst signal. Therefore, if there is any type of error in the enable signal EN1, an unwanted burst signal of the cable modem flows in the HFC network, causing the entire network to be shut down.